Concrete Technology (161-180)

Updated: Apr 29, 2020

161. The bond strength between steel and concrete is due to

both friction and adhesion

162. Impact strength of concrete increases by using

i) smaller maximum size of aggregate

ii) aggregate with low poisson's ratio


163. Impact strength of concrete is greater for angular crushed aggregates


164. If the contributions of tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetra calcium alumino ferrite to the 28 days strength of hydrated ordinary Portland cement are respectively W, X, Y and Z, then

W > X > Y > Z

165. The initial and final setting times for ordinary portland cement are approximately related as

T = 90+1.2t

where T and t are respectively final and initial setting times in minutes.

166 Assertion A : The presence of tricalcium aluminate in cement is undesirable.

Reason R : Tricalcium aluminate in cement contributes very little to strength of

cement.

Both A and R are true but R is not the correct explanation of A


167. Amount of gypsum required to be added to the clinker depends on the following contents of cement

i) tricalcium aluminate

ii) alkali

168. The diameter of needle used in Vicat's apparatus for the determination of initial setting time is prescribed as 1 mm

169. The heat of hydration of cement can be reduced by reducing the proportions of CA and CS

170. Increase in the fineness of cement results in

increase in the rate of heat of hydration without changing the total amount of heat liberated

171. Assertion A : Rapid hardening cement is generally not used in mass concrete

construction.

Reason R : The rate of heat development is low in rapid hardening cement.

A is true but R is false.

172. If the angularity number of an aggregate is increased, then the workability of the concrete using this aggregate will

decrease


173. If W₁, W, W and W are the weights of sand in oven dry, air dry, saturated but surface dry and moist conditions respectively, then the moisture content of sand is W₄-W₃


174. The ordinate of grading curve of an aggregate represents cumulative percentage passing each sieve plotted on normal scale

175. Increase in fineness modulus of aggregate indicates coarser grading

176. Weight of an oven dry sand and air dry sand are 500 gm and 520 gm respectively. If the weight of the same sand under saturated but surface dry condition is 525 gms, then the water absorption of sand is 5%

177. Soundness test of cement by Le Chatelier's apparatus gives unsoundness

due to free lime only

178. Maximum permissible limit of magnesia content in ordinary Portland cement is 6%

179. According to Indian Standards, the minimum 7 days compressive strengths of

ordinary Portland cement and portland pozzolana cement in N/mm2 are

respectively 21.5 and 21.5

180. According to Indian Standards, the pozzolana content in portland pozzolana

cement is 10% to 25%

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